最好用上not exists语句，虽然我知道别的方法一就可以找出来。还是拜托大神了。

搞笑你连表结构都不给怎么查？

你的意思是1号和2号任一门把，那就是下面了
select sno from grade where cno='01' or cno='02'

select sno from grade where cno='01' or cno='02' group by sno having count(sno)=2

那你能帮我看看我写的为什么就没结果呢。
select distinct sno from grade g1
where not exists(select sno from grade g2
where g2.cno='01' and not exists
(select sno from grade g3 where g3.cno='02'
and g3.cno=g1.cno and g3.cno=g2.cno));

如果硬要用not exists 我想到的就比较烦了
首先找到1，和2 都不选的学号
select sno from grade a where cno not in ('01','02') and not exists (select sno from grade b where a.sno=b.sno cno in ('01','02'))
然后再过滤掉1，和2 都不选的学号
最终就是
select sno from grade where cno not in (select sno from grade a where cno not in ('01','02') and not exists (select sno from grade b where a.sno=b.sno cno in ('01','02')))

换个思路：找出选了只选01 或只选了02 ，或者选了01和02的
select sno from grade where cno='01' or cno='02'
找出 只选了01，或者只选了02 的记录
select sno from grade where cno='01' or cno='02' group by sno having count(sno)=1
然后去掉只选了01，或者只选了02 的记录
最终就是
select sno from grade b where cno='01' or cno='02' and not esists (select sno from grade a where b.sno=a.sno and cno='01' or cno='02' group by sno having count(sno)=1
)

哈哈，我记得我当初听课，其实最难理解就是esists 其他都很简单；就是现在我的理解也就是
esists 用于可以多条件匹配， 而 in 只能单个条件匹配；就像你现在这个表，你只需要匹配sno就行了，所以完全可以用in 和not in 完成；

其实当你能够灵活运用sql语句的时候，真正难的不是编写语句；而是你解决问题的思路
越是复杂的问题，越是需要一步步解决，如果可以一下子想通解决的，那只是说明问题不够复杂；我接触的好几种语言感觉最简单的就是sql，语句的编写很适合人的阅读

select distinct sno from grade g1where sno in(select sno from grade g1 where g1.cno='01' and not exists (select * from grade g2 where g2.cno='02' and not exists (select * from grade g3 where g3.sno=g1.sno and g2.cno=g3.cno)));

我自己试过
正确的

select sname
from student
where not exists(select sno from sc where cno=1 and cno=2)

标准答案:
select sno
from grade
WHERE cno IN ('01','02')
GROUP BY sno
HAVING COUNT(1)<>1